1. Field of the Invention
The invention relates to joint compounds useful for filling and coating the joints between adjacent panels of wallboards. More specifically, it relates to reduced density joint compounds containing one or more rheology modification agents and one or more agents that produce stable air pockets.
2. Description of Related Art
Interior walls in residential and commercial properties are commonly constructed using inorganic wallboard panels or sheets such as gypsum wallboard (sometimes referred to as “wallboard” or “drywall”). Wallboards are usually prepared by enclosing a core of an aqueous slurry of gypsum and other additives between two sheets of paper. After the gypsum slurry has set and dried, the sheet is cut into standard industry sizes.
A wall is typically constructed by securing wallboards to a support structure. Screws or nails are commonly used to secure the wallboards to vertically or horizontally oriented pieces of wood. Joints are formed between adjacent wallboards. In order to conceal these joints and provide a smooth appearance to the wall, joint compounds are used to fill in the joints. Additionally, joint compounds are used to conceal the nail and screw holes formed in the wallboards, as well as any other surface indentations caused during transport or installation.
Joint compounds are commonly applied in several layers or coats. The first coat is placed into the joint using a wallboard knife, blade, or trowel. The first coat acts primarily to fill the space between adjacent wallboards. Joint tape can be embedded into the first coat of joint compound. Additional coats of joint compound can be applied to obtain a smooth finish. Each coat is allowed to dry and set prior to the application of the next coat. Failure to do so can lead to shrinkage or cracking. Sanding can be used to further smooth the surface.
Joint compounds can also be used for other purposes, such as repairing imperfections in building materials, adding textures to walls and ceilings, and so on.
Joint compounds can be supplied in the form of a dry powder, to which an amount of water is added at the work site by the applicators to give the joint compound a suitable consistency. Other joint compounds, often referred to as “ready-mix” or “ready-mixed” joint compounds, are pre-mixed with water and other additives during manufacturing the product. These joint compounds are generally packaged and sold in a corrugated box or plastic pail in a form that is suitable for use with little or no addition of water at the job site.
Among the prior art joint compound compositions, it is generally known to use a filler (e.g., calcium carbonate, calcium sulfate hemihydrate, or calcium sulfate dihydrate), thickener, preservative, and a binder, as well as various other additives to produce a joint compound, as disclosed in U.S. Pat. No. 5,653,797 (issued Aug. 5, 1997).
Many conventional joint compounds undergo shrinkage upon drying, which makes it difficult to achieve a smooth wall surface. Shrinkage can be particularly troublesome when a second coat of compound is applied over a previous coat that is not completely dried.
Conventional joint compounds tend to be fairly dense. While this may not be troublesome to a homeowner, commercial installers typically purchase and use 4.5 gallon (17 liters) pails of joint compound. The weight of such a large volume of compound can be considerable. Various attempts have been made to prepare joint compounds having reduced densities.
U.S. Pat. No. 6,476,099 (issued Nov. 5, 2002) offered a joint compound composition comprising a filler, a binder and a hydrocarbon substituted sulfate, sulfonate, sulfuric acid or sulfonic acid. The joint compound showed reduced shrinkage and was less likely to crack than conventional joint compounds.
U.S. Pat. No. 4,686,253 (issued Aug. 11, 1987) included expanded perlite in a joint compound. The perlite was coated to render it impervious to water. A general formulation was presented having a density of 6.9 pounds per gallon (0.83 kilograms per liter).
U.S. Pat. No. 4,454,267 (issued Jun. 12, 1984) discussed including expanded perlite treated with a silicone resin in joint compounds. The density of the joint compounds were generally about 8-9 pounds per gallon (0.96-1.1 kilograms per liter), and had viscosities of about 400-470 BU (Examples 1-6). Example 7 describes a joint compound prepared at plant scale, where the compound had a density of 13.97 pounds per gallon (1.67 kilograms per liter), and a viscosity of 700 BU.
U.S. Pat. No. 4,657,594 (issued Apr. 14, 1987) proposed a joint compound containing expanded perlite which is treated with an amino-functionalized siloxane or silicone polymer together with a silicone wetting agent. The density of the joint compound was 6.9 pounds per gallon (0.83 kilograms per liter), and the viscosity was 345 BU.
Despite developments made, there still exists a need for low density joint compounds that maintain attractive workability.